The glow is a textured plane with a white spot texture with alpha (BTW: beware of the the default conversion to 16bit that AE applies to textures. It somehow has a problem with alpha channels...i have to look into that) located in the middle of the diamond. The rubble is just a simple particle effect with particles using a rubble texture.

when does this 16 bit conversion occur ? when creating the texture or loading the image from resource ? i tend to load images with oldy class.getResourceAsStream(..) method as it's the most portable way

When uploading the texture to the GPU, i.e. at the latest possible stage. The rubble pieces are simple textured, billboarded triangles that act like as if they were emitted by a fountain...just like the stars in Robombs when you collect an item.

Added some stuff like score- and time counter, multi colored crystals, achievements...the only major thing that's still missing is a virtual opponent (like a ghost car in some racnig games).

Right now, i'm working to get a good "flow", i.e. to make the racing fun...not too easy and not too difficult, let a slow down feel just right, limit the jumps...that kind of stuff. The method that does the player's physics already looks pretty terrible...

The "ghost player" has been added in its basic form and some level decorations are in. Due to the latest improvements to the engine's core and some optimizations in the game's code itself, it isn't any slower than before.

It's not a skybox, it's just a bitmap blitted into the background. That's cheaper performance wise and for this game, it works just fine. If you have to use a real skybox or -dome, i tend to put the dome/box object in another world and render it in the same framebuffer. Just like i did with the skydome in this example: http://www.jpct.net/wiki/index.php/Advanced_example